You can disable the Flash uploader in your user preferences (or in the board options).

Ideally, we need to figure out what the error is. You may need to check your web server error logs for more details. If it's mod_security, you may be able to disable it by editing the .htaccess file (there's some code to enable in it) or by contacting your host.

As for the names, there are only usernames. You just signed up using your real name as your username.